After investigating this question for our exclusive report on Al Jazeera I can honestly say yes they are. Research by Jacqueline Stevens, a political scientist at Northwestern University, shows that up to one percent of all detainees at immigration detention centers are US citizens.

It's hard to know exactly how many citizens get deported every year. If that one percent figure was constant throughout all deportations – that would mean 4,000 US citizens a year are deported. While that's a high estimate, the fact that it's happening at all demands clear and urgent answers.

Stevens says it's an indicator of the abuses that are rife throughout the deportation machine.

"It's a symptom of the lawlessness of the deportation legal system. If US citizens go into the system with their full civil rights and they're unable to challenge their unlawful deportation that tells us a lot about the more precarious situation of everybody else who may not have the same rights as a citizen."

Criminal records

We met two deportees, Esteban Tiznado-Reyna and Andrés Robles.

Both have criminal records, which was the first thing immigration officials mentioned to us about them. It seems their rap sheet was more important than any chance they are citizens.

Esteban has been convicted of burglary, domestic violence and drug possession and Andres pleaded guilty to illegal entry of a property.

Despite their records, both also have strong evidence of their citizenship. Andrés's evidence was so strong that the government eventually let him back into the US and issued him with a passport card and certificate of citizenship.

The certificate says he became a citizen in 2002, six years before he was deported. But that was only after he spent nearly three years in Mexico.

An Immigration and Customs Enforcement, or ICE, spokesperson told us that Andrés never mentioned in his deportation hearing that he was a citizen. But he did mention it in his interrogation. Still ICE officials didn't look into his claims – despite viewing with him a photo of his father showing he was a citizen.

Andrew Free is Robles' lawyer. He says alarm bells should have sounded for those asking the questions during that interrogation but that it's hard to stop the deportation machine once it begins:

"When you look at the records that ICE created where Andres is claiming he's a US citizen, and then not three months later the US is putting him on a plane and walking him across the US-Mexico border, it seems that something had to have broken down."

Free also blames deportation quotas.

"Right now the Obama administration wants to deport 400,000 people per year. It wants to put 34,000 people in detention centres per night because Congress has mandated that," he said. "People were looking for a reason to detain him. That was what they were measured by and that's what the government and Andrés got."

Constant worry

Although he carries a passport with him everywhere he goes, Andres Robles is always looking over his shoulder. With his records still showing his deportation, he's worried he could be picked up and deported again at any time.

He's stuck in dead-end jobs. When employers do a background check on him his social security number shows he was deported. That kills any chance of getting legitimate work.

"I can't get certain jobs like welding. That's what I went to school for to weld. But when they look up my social security number it shows up that I'm deported."

So now he's suing the US government for $1.5m dollars and to have his record wiped clean of any mention of his deportation. Free says it could set a precedent, not just for people who were illegally deported, but perhaps for anyone looking to make a clean start – like terrorism suspects.

Esteban's case is less clear – he was born in Mexico, the son of a man who has a birth certificate from the state of Arizona. That would usually automatically make someone like him a citizen. But an immigration court ruled that the birth certificate, issued years after his father's birth, was not reliable.

ICE refused to sit down for an interview but said in a statement that his multiple criminal convictions made him a "priority for removal". The statement did not say whether or not he was a US citizen.

In 2008, Esteban beat a federal case against him that tried to prove he had entered the US illegally after one of his many deportations.

According to the jury he broke no law when he crossed into the US and - like any US citizen – had the right to enter the country. They weren't asked to decide if he was a citizen – but saying he had the right to enter the country implies that they recognise the strength of his claims.

Beaten by smugglers

Despite winning that case and convincing twelve jurors, Esteban still couldn't convince the most important authority - an immigration judge.

On April 12, he was deported - again. It's his sixth deportation.

Until he was released he was considering crossing back, a risky journey.

In the past, Esteban has been kidnapped in Mexico, beaten by smugglers and nearly died once of dehydration. Crossing the border has physically and mentally worn him down after years of deportations.

What's more, he crosses in one of the most dangerous parts of the border. An estimated 2,200 migrants have died along Arizona's stretch of the border since 2001. The real number is likely much higher.

"It stresses me out so much I get depressed because of what I’m going through crossing through the desert. They keep deporting me I think that’s not fair what they’re doing to me, kicking me out of my own country," he says.

Now back in Mexico, he questions whether he has the strength to make the crossing again – only to face a longer prison term than the last. He's overwhelmed by the thought of starting his life again at 40 and never being reunited with his family.

When we last saw him, he had decided to try his luck at getting work at a beach resort in northern Mexico. When he boarded a bus for the coast, he had about $200 in his pocket.